1. Field of the Invention
The present invention relates generally to a tensioner lever for a chain drive, and more particularly to a tensioner lever of the type using the resilient force of a torsion coil spring which urges a shoe surface of the tensioner lever against a chain to prevent the chain from becoming loose.
2. Description of the Related Art
In a chain drive used in an auxiliary device, for example, of an automobile engine for transmitting rotation between two or more spaced shafts, a tensioner lever is employed to remove the slack of a chain to thereby prevent whipping of the chain while running.
FIG. 9 shows one example of the conventional tensioner lever of the type concerned. The tensioner lever A1 is rotatably supported on a mount surface R of an engine body by means of a pivot shaft A2. A shoe surface S provided in a longitudinal direction of the tensioner lever A1 is adapted to be held in sliding contact with the outer circumferential surface of a slack run of an endless chain A3.
A torsion coil spring A5 is wound around and supported by a support pin A4 projecting from the mount surface A. The torsion coil spring A5 has one arm a engaged with a surface of the tensioner lever which is located on a side opposite to the shoe surface S. The other arm b of the torsion coil spring AS is in engagement with a retaining member Q provided on the mount surface R. By the force of the torsion coil spring S5, the tensioner lever A1 is urged to turn about the pivot shaft A2 in the clockwise direction shown in FIG. 9. As a result, the shoe surface S presses or forces at all times the outer peripheral surface of the chain slack side toward the interior side of the chain A3, thereby preventing the chain from becoming loose.
FIG. 10 shows another example of the conventional tensioner lever. The illustrated tensioner lever B1 has the same function as the tensioner lever A1 show in FIG. 9 but differs therefrom in that a torsion coil spring B3 used for urging a shoe surface S against a chain B2 has a helically coiled portion supported concentrically with a pivot shaft B4 on which the tensioner lever B1 is rotatably supported with respect to a mount surface R.
As clearly shown in FIG. 11, the tensioner lever B1 has a boss B5 projecting toward the mount surface R. The coiled portion of the torsion coil spring B3 is fitted around the boss B5. One arm axe2x80x2 of the torsion coil spring B3 is engaged with the tensioner lever B5, and the other arm bxe2x80x2 of the tensioner lever B1 is engaged with a spring retainer pin B6 projecting from the mount surface R.
In the conventional tensioner lever 9 show in FIG. 9, since the torsion coil spring A5 and the spring support pin A4 are disposed on a side of the tensioner lever A1, these parts requires an installation space on the mount surface R which is provided on the exterior side of the endless chain A3.
In the conventional tensioner lever B1 shown in FIGS. 10 and 11, since the torsion coil spring B3 is supported on the pivot shaft B4 together with the tensioner lever B1, a space for installation of these parts on the mount surface R is relatively small. However, due to the provision of the boss B5 disposed between the tensioner lever B1 and the mount surface R, the overall height of the tensioner lever B1 as measured from the mount surface R is made large.
Additionally, in the foregoing conventional tensioner levers, since the torsion coil spring is assembled with the tensioner lever when the tensioner lever is mounted to the mount surface, the assemblage of the conventional tensioner levers is relatively low in efficiency.
It is therefore an object of the present invention to provide a tensioner lever for chain drives, which requires only a small space for installation to a mount surface and can be easily and speedily assembled onto the mount surface.
To attain the foregoing object, the present invention provides a tensioner lever for a chain drive including an endless chain driven to travel over a mount surface, wherein the tensioner lever comprising: a lever body pivotally mounted at one end to the mount surface by means of a pivot shaft, the lever body having a shoe surface extending in a longitudinal direction thereof; and a torsion coil spring acting between the mount surface and the lever body and urging the lever body to turn about the pivot shaft in a direction to move the shoe surface into pressure contact with the chain. The lever body has an internal space formed therein for accommodating within it at least a coiled portion of the torsion coil spring, the internal space having an opening for enabling the torsion coil spring to be assembled in the internal space. The lever body further has a boss disposed inside the internal space and having an axial hole through which the pivot shaft extends and an outer peripheral surface around which the coiled portion of the torsion coil spring is loosely fitted, the axial hole and the outer peripheral surface being concentric with each other.
With this construction, since at least the coiled portion of the torsion coil spring is disposed inside the lever body, there is no need to provide a space on the exterior side of the lever body for installation of the torsion coil spring. By virtue of this, the tensioner lever can be mounted on a relatively narrow mount surface.
It is preferable that the lever body includes a spring engagement portion engageable with a portion of the torsion coil spring to keep the torsion coil spring in position against removal from the lever body through the opening. Since the torsion coil spring is stably held or assembled on the lever body, the lever body can be readily mounted to the mount surface. Additionally, since the lever body and the torsion coil spring assembled thereon can be treated as a preassembled single part, storage, transportation and other processing of the parts can be achieved simply less costly.
In one preferred form, the lever body has a peripheral wall forming the internal space and a cutout portion formed in a part of the peripheral wall. The torsional coil spring has an arm contiguous with one end of the coiled portion and being anchored to the mount surface, the arm extending through the cutout portion to the exterior side of the lever body. The spring engagement portion is comprised of an engagement recess formed in the peripheral wall at one end of the cutout portion for retaining therein a portion of the arm when the arm is urged toward the one end of the cutout portion by the resiliency of the torsion coil spring before the arm is anchored to the mount surface. With the arm part thus retained in the engagement recess, assemblage and replacement of the torsion coil spring relative to the lever body can be achieved with utmost ease.
In another preferred form, the lever body has a peripheral wall forming the internal space, the torsion coil spring has an arm contiguous with one end of the coiled portion and being anchored to the lever body, and the spring engagement portion is comprised of a wing-like spring retaining piece projecting from the peripheral wall into the internal space at a portion adjacent to the shoe surface for retaining thereon the arm of the torsion coil spring. The spring engagement piece projecting from the peripheral wall of the lever body is simple in construction and can be formed integrally with the lever body by die-casting or synthetic resin molding.
In still another preferred form, the spring engagement portion is comprised of at least one radial engagement projection formed on the outer peripheral surface of the boss at an end adjacent to the opening, the radial engagement projection having an outside diameter larger than an inside diameter of the coiled portion of the torsion coil spring. The torsion coil spring is stably held within the internal space of the lever body with the coiled portion retained on the radial engagement projection.